Maybe this is a security concern so it might not be in the realm of possibilities, but I'm trying to emulate the client side portion of cookies in a plunk (for client only, you can just use localStorage, but I'll plumb up the cookie sending/receiving bits on my own server)

The problem is, setting a cookie seems to invalidate any subsequent requests (which will also send that cookie to the server). I'm guessing the server doesn't like receiving cookies it doesn't have any knowledge of, but it's probably welcome to not read those anyway. In either case, after the initial load, all subsequent requests will return:
Oh dear, something didn't go quite right
Bad Request
Here's a trivial plunk that displays this issue:
https://plnkr.co/edit/8mKpTFl3u8R63fGF8yaj
It'll work the first time before the cookie has been set (testable in incognito window), but all subsequent requests will cause issues when the cookie is sent to the server
